This invention relates to heavy duty pipe straightening machines in general and more particularly to mobile pipe straightening machines of the roll straightening type and which are particularly suited for use in the field.
Heavy duty pipe straightening machines historically have evolved from an ancient form using gag press principles to present day machines using spin straightening principles and roll (or cross-roll) straightening principles. A pipe straightening machine using the gag press principles, in simplified terms, incorporates a pair of spaced blocks for supporting the pipe and an overhead ram for exerting a transverse force on the pipe at a point intermediate the blocks. The pipe is bent in the transverse direction beyond straightness such that when the transverse pressure is removed, the pipe ideally is straight. This procedure, although having many advantages, also has disadvantages. For example, it crimps the pipe and repeated use puts a series of smaller bends in the pipe. The procedure also undesirably sets up stresses within the structure which usually cause microscopic cracks to develop, thereby weakening the pipe structure.
In an attempt to alleviate some of the problems associated with gag press principles, heavy duty machines using spin straightening principles evolved. These machines incorporated a series of lower drive rolls in combination with a series of overhead idler rolls. The respective rolls had contoured surfaces to accommodate the particular size of the pipe needing straightening. Rather sophisticated equipment was attached to the ends of the pipe for exerting pressures thereto which placed the pipe in tension. The equipment then caused the pipe to spin as it traversed between the lower and upper rolls. Such machines were not adapted for universally accommodating wide ranges of pipe diameters without changing of the rolls to ones having the proper surface contours.
Such pipe straightening machines using the described spin straightening principles have found generally satisfactory use in mills. Mills generally have high volumes of pipe having the same outside diameter and such ameliorates the characteristic of being non-universal. Also, spin straightening machines are ordinarily exclusively stationery in nature at the mills. Thus the fact that such machines were of unduly large weights and size was of little significance to mill usage.
To overcome the non-universal characteristic of spin straightening machines, the roll, or cross-roll, pipe straightening machines developed. These machines utilized lower drive rolls and upper idler rolls which were at a skewed orientation or angle with the axis formed by the passage of the pipe between the rolls. By adjusting the amount of skew, a wide range of pipe diameters could be accommodated without replacing the particular drive and idler rolls. Also, the roll type straighteners did not require the pipe needing straightening to be placed in tension.
Generally such roll straightening type pipe straightening machines also found applications in mills. Accordingly, the weights and sizes of such machines were often enormous, effectively preventing their being transportable for field applications.
Pipe straightening machines of the roll straightening type have now been developed capable of being transported to the field for straightening drill pipe. Once such machine is described in Canadian Pat. No. 831,323, entitled PIPE STRAIGHTENER, issued to Walter A. Johnson on Jan. 6, 1970. Although this pipe straightening machine was a considerable advance forward, it suffered from several drawbacks. It was unneedlessly heavy for the size of pipe it accommodated, thereby being unduly difficult to transport in the field. The machine basically incorporated the basic concepts of the spin straightening machines in regard to the support structure for the upper and lower rolls. Accordingly, this machine utilized upper and lower, heavy duty yokes which were pivotally connected by tension rods. The top and bottom rolls were respectively supported by the yokes, and the top rolls were adjusted by mechanisms overlying the top yoke. This assemblage was restrictive in transportability and operation not only because it resulted in an unnecessarily heavy machine, but also one of unnecessary height, thereby unnecessarily increasing the height of the center of gravity.
Such prior roll straightening type machines developed for field application also suffered from their inability to roll straighten the upset ends of drill pipe when they became bent (referred to as hooked ends). The pipe straightener described in the above Canadian patent utilized a form of a reverse gag press in an attempt to straighten hooked ends, but suffered from the same drawbacks above enumerated for early pipe straightening machines of the gag press type. Furthermore, such machines for field usage had no ability to allow visual inspection of the pipe while the pipe was still in the machine. This not only was a time consuming disadvantage, but also was frustrating to operators of the machine.